Navigation systems and the like of recent years assist various kinds of driving operations such as deceleration assistance for a driver of a vehicle that travels around an intersection where a traffic light is provided or around traffic elements such as a curve for example. Such a navigation system acquires information representing existence of a traffic element or a phase cycle of a traffic light, which require a decelerating operation, from infrastructure information or road traffic information sent from an infrastructure communication device provided on a road or a road traffic information center for example, and assists a driving operation such as deceleration assistance based on the acquired information.
According to a device described in Patent Document 1 for example, a driving pattern of a vehicle (subject vehicle) that travels on a road is previously classified into a speed changing pattern when a traffic light shows red phase and a speed changing pattern when the traffic light shows green phase, and the classified speed changing patterns are stored in a storage device provided in the vehicle. This device acquires information representing speed and the like of a vehicle in front which travels in front of the subject vehicle in the traveling direction, and identifies to which one of the speed changing patterns stored in the storage device the transition of speed of the vehicle in front indicated by the acquired information corresponds. If this device identifies that the speed changing pattern of the vehicle in front is the speed changing pattern in the green phase of the traffic light, the device determines that necessity of deceleration or stop is low and suppresses execution of deceleration assistance. According to this, the device described in Patent Document 1 assists the driving operation in accordance with the phase of a traffic light without using information related to a phase cycle of the traffic light.